Acrylonitrile-butadiene-styrene copolymer resin (hereinafter ‘ABS resin’) is a graft-copolymer resin (hereinafter ‘g-ABS’) in which styrenic monomers and acrylonitrile monomers are grafted with a butadiene-based rubbery polymer dispersed in a styrene-acrylonitrile copolymer resin (hereinafter ‘SAN resin’) which is a matrix copolymer. ABS resin has excellent impact resistance, chemical resistance, heat resistance and mechanical strength, is readily molded, and accordingly is widely used in the manufacture of components for electric and electronic goods, interior/exterior construction materials, automobile parts, and miscellaneous goods, among other products.
A recent trend is to paint plastic molded products, such as electric and electronic goods, to improve their external appearance, polishing properties, surface-scratch resistance and weather resistance and to provide high-quality products with a luxurious appearance. As used herein, reference to painting a resin surface includes the application of paint, metal, or other coating materials using any suitable technique, including without limitation metal deposition.
Generally, the surface of the resin product is pretreated or primed prior to painting to improve adhesion of the coating material and surface appearance of the end product. For example, when ABS resin is used as a back-ramp housing material for an automobile, the surface of an ABS injection molded product is typically pretreated or primed prior to metal (such as aluminum) deposition by smoothing the surface of the injection-molded product using chemical solvents. The surface of the resin must be properly prepared to provide the desired degree of gloss after aluminum deposition.
Generally, the chemical resistant property or paintability of ABS resin can be improved by regulating the acrylonitrile content in the ABS resin. For example, increasing acrylonitrile content can prevent stress cracks caused by solvents. However, the coating film may be stripped off. On the other hand, if the acrylonitrile content is too low in the ABS resin, the external appearance of the resultant product can deteriorate due to coating corrosion by solvents, thereby requiring a double coating process. Hence, there is a need to improve paintability of the ABS resin.
Polyester resin has a short molecular chain and a structure that is not easily bent so that it has good stiffness properties, electric properties, weather resistance and heat resistance and its tensile strength is rarely decreased when exposed to high temperature for a long time. Also, the polyester resin has good tolerance to oil like diesel oil and has high dimensional stability and moldability so that it is widely used in various industrial fields such as automobile parts and electric and electronic goods, among others. Furthermore, polyester resin is suitable for use as a material for a head-ramp bezel of an automobile because molded products formed thereof can have a graceful surface, excellent polishing property and paintability, for example, excellent adhesive property with regard to vacuum deposited aluminum or chromium coating. The physical properties of polyester resin, however can easily change when the resin is exposed to acid or alkali at high temperature for a long time because of its ester bonds in the molecular chain.